Homogeneous bulk polymerization of ethylenic unsaturates in the presence of diazo-thio-ethers



Patented Mar. 28, 1950 HOMOGENEOUS BULK POLYMERIZATION 0F ETHYLENICUNSATURATES IN THE PRESENCE OF DIAZO-THIO-ETHERS William B. Reynolds,Bartlesville, 0kla., and Ernest W. Gotten, deceased, late ofBartlcsville, Okla., by Richard K. Harris, administrator, Bartlesville,0kla., assignors to Phillips Petroleum Company, a. corporation ofDelaware No Drawing. Application February 16, 1948, Serial No. 8,735

13 Claims.

This invention relates to the polymerization of unsaturated organiccompounds capable of undergoing an addition polymerization to form highmolecular weight polymers. mom of its more specific aspects it relatesto the polymerization of an aliphatic conjugated diene hydrocarbon,including substituted derivatives, either alone or in admixture with a.monomer copolymerizable therewith to form long chain polymers of thetype known as snythetic rubbers. In a still more specific aspectit'relates to the polymerization of a butadiene-1,3 hydrocarbon, or of aderivative thereof, such as chloroprene, in a homogeneous system in thepresence of an improved initiator for the polymerization reaction. Thisapplication is a continuation-in-part of copending application SerialNo. 641,866, filed January 17, 1946.

Unsaturated organic compounds capable of undergoing an additionpolymerization to form high molecular weight polymers may beadvantageously polymerized, in accordance with the present invention, ina homogeneous system. Such unsaturated organic compounds are generallythose which contain a methylene group attached by an olefinic doublebond to a carbon atom in the structure CH2=C Compounds which contain theCH2=C group and are suitable as monomers for use in the process of ourinvention include the following: 1,3-butadiene and its homologues andanalogues which polymerize in the same manner, such as isoprene,piperylene, chloroprene, and the like; styrene; acrylonitrile; methylacrylate; methyl methacrylate; vinyl chloride; etc. These unsaturatedorganic compounds are given by way of example only. The unsaturatedorganic compounds may be polymerized alone or in admixture with othermonomers copolymerizable therewith.

When the aforementioned materials, either singly or in admixture withother polymerizable substances, are allowed to stand in a closedcontainer, polymerization occurs with the resultant formation of variouspolymeric products. However, the rate of reaction is generally veryslow, a period of several days or even weeks frequently being requiredto reach complete conversion. While in some instances the presence ofoxygen or an oxygen-containing compound such as, for example, benzoylperoxide or other similar material is known to increase thepolymerization rate, the conversion of these unsaturated organiccompounds to polymeric products is still a relatively slow process.

A method has now been found whereby the rate of polymerization ofpolymerizable organic compounds in a homogeneous liquid system ismarkedly increased and polymeric products of excellent processabilityare obtained. In accordance with the present invention polymerization iseffected in the presence of a small quantity of a diazo thioether,preferably anoil-soluble diazo thioether, which exerts a pronouncedacceleratiIlg effect on the conversion rate and also serves as amodifier for the polymerization.

An object of this invention is to provide an improved process for theaddition polymerization of unsaturated organic compounds to form highmolecular weight polymers. Another object is to provide an improvedprocess for the polymerization of aliphatic conjugated dienehydrocarbons. Another object is to provide an improved process for thecopolymerization of a butadiene hydrocarbon and a monomercopolymerizable therewith in a homogeneous system. Still another objectof this invention is to provide improved initiators or catalysts for usein polymerization reactions of this type. A further object of thisinvention is to provide compounds particularly suited as initiators andmodifiers in homogeneous, or bulk, polymerization of polymerizableorganic compounds. A still further object is to provide improved highmolecular weight polymers of unsaturated organic monomers. An importantobject of this invention is to provide a polymerization process in whicha novel initiator is employed to effect a reduction in the time requiredfor carrying out polymerization reactions of this type. Further objectsand advantages of this invention will become apparent, to one skilled inthe art, from the accompanying disclosure and discussion.

The diazo thioethers employed in this invention have the generalstructural formula RrN=N-S--R' where R is a member of the groupconsisting of aromatic and substituted aromatic radicals and R. is amember of the group consisting of aromatic, substituted aromatic,cycloalkyl, substituted cycloalkyl, aliphatic, and substituted aliphaticradicals. These compounds, which may be conveniently prepared bydiazotizing an aromatic amine and coupling the diazonium compound withan aliphatic or aromatic mercaptan, are more fully described in thepreviously mentioned application of Reynolds and Cotten, Serial No.641,866, filed January 17, 1946.

Examples of aromatic amines which may be used in the preparation of theoil soluble diazo thioethers are: aniline, chloroaniline, bromoaniline,toluidine, anisidine, phenetidine, 4-aminodiphenyl ether, dimethoxyaniline, methylmethoxy aniline, trimethyl aniline, dichloroaniline,xylidine, chlorotoluidine, a naphthylamine, dianisidine, benzidine,dichlorobenzidine, etc. Examples of mercaptans that may be used as acoupling component are: thiophenol, thiocresol, chloro thiophenol,methoxy thiophenol, thioalphanapthol, thio-beta-naphthol, n-butylmercaptan, tert-butyl mercaptan, cyclohexyl mercaptan,mercaptobenzothiazole, octyl mercaptan, and the like. Preferably,neither the amine nor the mercaptan will contain more than eighteencarbon atoms per molecule.

The diazo thioethers preferred for use as polymerization catalysts inaccordance with the present invention are those in which both R and R inthe foregoing structural formula are aromatic or substituted aromaticgroups. Examples of preferred compounds are substituted benzene diazomercapto-naphthalenes, substituted benzene diazo mercapto-benzenes,substituted naphthalene diazo mercapto-benzenes, and substitutednaphthalene diazo mercapto-naphthalenes. Preferred substituent groupsare the aikyl, alkoxy, aryloxy (e. g., phenoxy), carboxy, sulfo (SOaH),halo, and nitro groups. Other substituents give diazo thioethers ofvarying degrees of usefulness.

The diazo thioethers can conveniently be prepared by diazotizing anaromatic amine and coupling the diazonium compound with an aliphatic oran aromatic mercaptan. Diazo thioethers containing two diazo thioethergroupings can be prepared by tetrazotizing an aromatic diamine andcoupling the tetrazonium compound with two molecular equivalents of amercaptan. The coupling to the mercaptan is usually carried out in astrongly alkaline medium although in some examples it is advantageous tocarry out the coupling in weakly acidic media. The crude diazothioethers isolated from the coupling are usually of suflicient purityfor use in polymerization reactions. However, if a purified-product isdesired the oil-soluble types may be purified by dissolving in acetoneor anhydrous ether at about C., cooling to about --50 C. and filteringof! the recrystallized product. The water-soluble type diazo thioethers,in the form of their ammonium or alkali metal salts (resulting fromcoupling in an alkaline medium) ,can be conveniently purified by washingwith anhydrous ether.

Compounds which are preferred catalysts for the polymerization processof this invention are those represented by the formula ArN=N-SR' 1).where Ar is an aryl group and X is a substituent selected from the groupconsisting of alkyi, alkoxy, aryl and aryloxy radicals, n is an integerfrom one to four, 11. being at least two when a methyl radical is asubstituent; and R is a member of the group consisting of aromatic,substituted aromatic, cycloalkyl, substituted cycloalkyl, aliphatic, andsubstituted aliphatic radicals. When a methyl substituent is employed inthe aryl group attached to the nitrogen at least one other methyl (orother alkyl), alkoxy, aryl, or aryloxy radical is also present. Specificexamples of such compounds are the following: 2-(4 methoxybenzene diazomercapto)-naphthalene, 2-(4-methylbenzene diazo mercapto)-naphthalene,2- (2,4-dimethylbenzene diazo mercapto)- naphthalene, 2-(4-chlorobenzenediazo mercapto)-napthalene, l-(4-methoxybenzene diazo mercapto)-naphthalene, 1- (2,4-dimethylbenzene diazo mercapto) naphthalene, 2-(4-chlorobenzene diazo mercapto) -2-methy1 propane, and the like,together with the ammonium and alkali metal salts of such compounds.Some of the more important new compounds may be conveniently representedby the formula where X is a substituent selected from the groupconsisting of alkoxy and aryloxy radicals, n is an integer from one tofour, and R is a member of the group consisting of aromatic, substitutedaromatic, cycloalkyl, substituted cycloalkyl, aliphatic, and substitutedaliphatic radicals.

When operating according to the process of this invention, apolymerizable organic monomeric material, either alone or in admixturewith a monomer copolymerizable therewith, is charged to anyconventional-type reactor, together with the requisite quantity of diazothioether, with which it has previously been admixed or, if desired, thediazo thioether may be introduced into the reactor following charging ofthe polymerizable material. Following the charging procedure thetemperature is adjusted to the desired level and the reaction mixture isstirred, or otherwise agitated, until the desired degree of conversionhas been attained. In some instances it is preferred to irradiate thereaction mixture with actinic light in order to increase thepolymerization rate. When carrying out polymerization reactionsaccording to the process herein described, an inert solvent may be usedand in some instances it is preferred to so operate. Among the solventswhich are applicable may be mentioned paraflln hydrocarbons, such as abutane, a pentane, or a hexane, cycloparamns such as cyclohexane, andaromatic hydrocarbons, such as benzene or mixtures of such hydrocarbonsor derivatives thereof. The polymer is recovered from the reactionmixture in any suitable manner, e. g., by coagulation with alcohol, bytreatment of the reaction mixture with boiling water to remove unreactedmonomers, filtration and subsequent drying of the polymer, or by removalof the unreacted monomers at slightly elevated temperatures undervacuum.

The rate of polymerization of polymerizable organic compounds in ahomogeneous system, and also the degree of modification of the polymericproduct, are controlled in large part by the amount of diazo thioetherpresent. Another factor which affects the conversion rate is thetemperature maintained during the polymerization period. The amount ofdiazo thioether employed will usually range from about 0.05 to about 5.0per cent by weight, based on the quantity of unsaturated organicmaterial employed. The degree of modification obtained increases as theamount of diazo thioether is increased. Polymerization temperatures willusually vary from about 10 to about 70 0., although lower temperaturesare applicable in cases where it is desirable to so operate. In someinstances temperatures as low as about -30 C. may be employed. The diazothioether may be added in increments throughout the polymerizationreaction, in order to provide more uniform results and more eflicientutilization of the diazo thioether.

The use of diazo thioethers in polymerization reactions of the typeherein described represents a definite advance over the art. Whilecatalytic effects have been observed when reactions of this type arecarried out in the presence of oxygen,

or oxygen-yielding compounds such as peroxides, run carried out withbenzoyl peroxide gave a, 16 e. g., benzoyl peroxide, the reaction rateis much per cent conversion.

more rapid when diazo thicethers are employed.

In addition, diazo thioethers also exert a modify- Example 1v ing effecton the polymer and a means of con- 5 Two polymerization...) are eflectedi the a trolling polymer propertie i thus aflel'dedner referred to inExample 1 except that in one one of the greatest advantages of the useor case 0.3 per cent 2- (4-methylbenzene diazo merdiazo thioethers inpolymerization reactions in captmmaphthmene is added and m the otheraccordance with our invention is their great verthe same quantity of 4dimethylbenzene db satility. Diazo thioethers of almost any desired 82mercapto) naphfllalene is employed 'fi can be Prepared by suitablyVarying, the When the polymerization temperature is held at zz i ij ggggg gg gg s ggg g fi gsg gi 50C. the results are comparable to that when2-(4-m th activity can be obtained if either or both of the thaleneeis azgf diazo mercapto) naph radicals contain activating substituents, forex-' M ample, alkyl or alkoxy groups. If low-activity E mplev initiatorsare desired for polymerization reactions The polymerization ofchloroprene 1 eflected at higher temperatures the radicals R and R can ith presence of 03 per t 1-(4-methoxybencontain deactivatingsubstituents, for example, zene di mercapto) h t 1 The chloro 0r nitrO pWhen is aliphatic, cedure followed is the same as that described indiazo thioethers of high ac v y are ebteined- Example I.. Thetemperature is maintained at Considerable variation in this highactivity can 50 C. throughout the polymerization. At the end he obta nedy Varying the Substitllehts 0n the of a 10-hour period, the conversionreached is 32 aromatic radical R. per cent. When a similar reaction iscarried Advan a s Of t invehtien are illustrated 25. out in which thediazo thioether employed is by t e f llowi e a pl s. The reac n s, and2-(4-chlorobenzene diazo mercapto)-2-methyl their prepeltlens, end theother Specific propane, comparable results are obtained. gredients ofthe recipes, are presented as being typical and should not be construedto limit the Example VI invention unduly A butadien-styrene copolymerwas prepared Example I from 75 parts butadiene and 25 parts styrene.

The reaction was effected at 50 C. in the presence Two chloroprenepolymerizations were carried of 2,7 parts 2-(4-methoxybenzene diazo OutSimultaneo sly in homogeneous y capto) -naphthalene. The procedurefollowed T e a e qua y f hl ropre e wa cha ed o was essentially thatdescribed in Example I. A each of W reactors- I One reactor Wes 40 percent conversion was reached at the controduced 0.3 per cent2-(4-methoxybenzene diazo chlsion of a 32- reaction period mercapto)-naphthalene while to the other 0.3 per cent benzoyl peroxide was added.The tempera- 40 x pl VII ture was maintained at C. throughout thepolymerization period. The liquid reactants were figf i g gg g gg gfiffi fig tg' gig gz mildly agitated the run containing the diazo to standat room temperature in the presence of thlqether 198mg allowed continuefor a 124mm. actinic light. The material polymerizes to a solid periodwhile that containing the benzoyl peroxide mass of olyst rene in fl hwas allowed to react for 16 hours. At the conp y W oursclusion of thepolymerization the polymer was re- Example VIII covered by treating thereaction mixture with boiling water, filtering, and drying the product.A 46 per cent conversion was reached in the diazo methexybenzene diazo een p thioether run while a conversion of only 25 per 0 thalene ispolymerized a C. The material cent was obtained in the run containingbenzoyl is mild? a d during the 20-hour reaction peroxide. The samplecontaining the diazo thioperiod. At the end of this time a solid polymerether was soft and well modified while that in is formed.

Methyl methacrylate containing 0.5 per cent which the benzoyl peroxidewas used was tough Example IX and difllcult to process. 1

. A 50 per cent solution of vinyl chloride in ben- Ezample II zene ischarged to a reactor and 0.5 per cent 2- I (4-methoxybenzene diazomercapto) -naphtha-.

chlereprene was p yme in the presence le'ne added. The mixture isagitated 20 hours at of 0.15 P r cent 2-(4-methoxybenz diazo atemperature of 50 C. Recovery of the polymer capto)-naphthalene usingthe procedure of Ex: is eflected by removal of t solvent and ample I.The temperature was maintained at 50 reacted monomer at a slightlyelevated tempem C. At the end of a 10-hour Period conversion t re undervacuum had reached 27 per cent. A parallel run made in the presence of0.15 per cent benzoyl peroxide Example x gave all) per cent conversionFour similar reactors were each charged with Example chloroprene and2-(4-methoxybenzene diazo mercapto) naphthalene, referred to as MDN. As

The procedure of Example I was followed f0! indicated in the followingtable, a, different the polymerization of chloropren pt that amount ofthis diazo thioether was used in each 0- P r cent h X en e diazo mrreactor. The reaction was conducted, with agitacapto) -naphthalene wasused instead of 0.3 per ti n, at 50 c, nd t va i i t r l samples cent. A34.5 per cent conversion was reached at were secured from the reactorsto determine the the end of a 10-hour reaction period. A similar llextent of polymerization of the chloroprene. The

. 6.76 hours.

asonees data so obtained are presented in the accompany table.

SampleNo i 2 3 4 Parts MDN 0.075 0.15 0.30 0.45

4.25 hours 4.75 hours.

6.6 hours. 10.0 hours.

7! 2-(4-mcthoxybcnzene diazo mercapto)-naphthalene.

It is interesting to note that the conversion curves defined by thesedata are not linear with respect to time. Over the range 0.15-0.45 partMDN the conversions at a given time are linear functions of the initialconcentration of MDN. However, conversions with 0.075 Dart MDN do notfall on these straight lines and extrapolated values at zero MDN arehigher than the previously obtained uncatalyzed rates. Therefore, itmust be assumed that the linear relationship holds only over a limitedrange oi catalyst concentrations. 4

The polymers produced with MDN catalysis in these runs appeared to beover-modified.

As will be evident to those skilled in the art;

various modifications of this invention can be made, or followed, in thelight of the foregoing disclosure and discussion, without departing fromthe spirit or scope of the disclosure or from the scope of the claims.

What is claimed is:

1. An improved method for producing a synthetic rubber comprisingpolychloroprene, which comprises polymerizing chloroprene in a liquidhomogeneous bulk system at a polymerization temperature between 10 and50 C. in the presence of 0.05 to 5 per cent by weight of2-(4-methoxybenzene diazo mercapto)-naphthalene as polymerization'catalyst, and recovering an elastic polymeric material as a product ofthe process.

2. An improved process for the polymerization of chloroprene, whichcomprises agitating a liquid homogeneous bulk reaction mixturecomprising chloroprene at a polymerization temperature betion in thepresence of a diazo thioether of the formula R-N=N-BR' where R is anaromatic radical and R is selected from the group consisting oiaromatic, cycloallphatic, and aliphatic radicals. and each of R and R'contains not more than eighteen carbon atoms. a

4. In a process oi polymerizing by addition polymerization anethylenically unsaturated polymerizable organic compound to form a highmolecular weight linear polymer while in a liquid bulk homogeneousreaction mixture to produce an elastic polymer of high molecular weight,the improvement which comprises incorporating in such a .reactionmixture and eiiecting said polymerization reaction in the presence ofbetween 0.05 and 5 per cent by weight of a diazo thioether, oi theformula RN=NSR' where R is an aromatic radical and R is selected fromthe group consisting of aromatic, cycloaliphatic, and aliphaticradicals, and each of R and R contains not more than eighteen carbonatoms.

5. The improvement of claim 4 wherein said diazo thioether is amethoxybenzene diazo mercapto-naphthalene.

6. The improvement or claim 4 wherein said diazo thioether is a4-methoxybenzene diazo mercapto-naphthalene.

7. The improvement of claim 4 wherein said diazo thioether is2-(4-methoxybenzene diazo mercapto) -naphthalene.

8. The improvement of claim 4 wherein said diazo thioether is1-(4-methoxybenzene diazo mercapto) --naphthalene.

9. The improvement of claim 4 wherein said polymerizable ethylenicallyunsaturated organic compound is chloroprene and said diazo thioether isa methoxybenzene diazo mercapto-naphthalene.

10. The improvement of claim 4 wherein said polymerizable ethylenicallyunsaturated organic compound is 1,3-butadiene and said diazo thioetheris a methoxybenzene diazo mercapto-naphthalene.

11. The improvement of claim 4 wherein a mixture of butadiene andstyrene are copolymerized and said diazo thioether is a methoxybenzenediazo mercapto-naphthalene.

12. The improvement of claim 4 wherein said diazo thioether is achlorobenzene diazo mercapto-paraflln.

13. The improvement of claim 4 wherein said diazo thioether is2-(4-chlorobenzene diazo meracpto) -2-methylpropane.

WILLIAM B. REYNOLDS. RICHARD K. HARRIS,

5:, Administrator of the Estate of Ernest W. Gotten,

Deceased.

No references cited.

3. IN A PROCESS OF POLYMERIZING BY ADDITION POLYMERIZATION ANETHYLENICALLY UNSATURATED POLYMERIZABLE ORGANIC COMPOUND TO FORM A HIGHMOLECULAR WEIGHT LINEAR POLYMER WHILE IN A HOMOGENEOUS BULK FLUIDREACTION MIXTURE, THE STEP WHICH COMPRISES INCORPORATING IN SUCH AREACTION MIXTURE AND EFFECTING SAID POLYMERIZATION REACTION IN THEPRESENCE OF A DIAZO THIOETHER OF THE FORMULA R-N=N-S-R'' WHERE R IS ANAROMATIC RADICAL AND R'' IS SELECTED FROM THE GROUP CONSISTING OFAROMATIC, CYCLOALIPHATIC, AND ALIPHATIC RADICALS, AND EACH OF R AND R''CONTAINS NOT MORE THAN EIGHTEEN CARBON ATOMS.